United States Patent
`
`
`
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`Alcivar
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`
`
`(19)
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`
`
`[11]
`3,746,789 ©
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`[45] July 17, 1973
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`[75]
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`[54] TISSUE CONDUCTION MICROPHONE
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`
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`UTILIZED TO ACTIVATE A VOICE
`OPERATED SWITCH
`
`
`Inventor: Ernesto A. Alcivar, Guayaquil,
`
`
`
`Ecuador
`
`[73] Assignees: Dennis J. Johnson, Swampscott;
`
`
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`
`
`
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`
`
`Brian N. McCarthy, Cambridge,
`
`Mass.
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`
`
`
`Oct. 20, 1971
`[22] Filed:
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`
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`[21] Appl. No.: 191,006
`
`[56]
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`[57]
`[52] US. Ch ceccsesssesesscesenscstseeseees 179/1 VC
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`A voice-activated transmit switch (VOX) for high
`[51] Unt. Che oc ccccsesesscasssseceseeeseere G101 1/04
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`noise environment voice
`communication systems
`[58] Field of Search............ 179/1 VC,
`1 SW,
`1 SA,
`
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`which empioy a speech microphone, a transmitter and
`179/121 C, 167, 168, 164, 187, 188,
`1 P,
`1
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`a receiver. A separate tissue-conduction microphoneis
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`VW, 157,
`1 ST; 340/8 R,5 R,5 T
`employed to generate a signal which activates a trans-
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`mitter enabling and receiver disabling circuit. The tis-
`References Cited
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`sue-conduction microphone is positioned in contact
`
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`with the user’s necktissue in the vicinity of the larynx.
`UNITED STATES PATENTS
`
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`A bandpassfilter eliminates the unwanted signal from
`2/1916 Forest... cccsccscscsetecsseensee 325/22
`1,170,882
`
`
`
`
`
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`the tissue-conduction microphone output and passes
`
`
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`2,374,090
`» 179/1 AL
`4/1945
`French......
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`
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`the desired speech signals to an amplifier. The ampli-
`
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`3,292,618=12/1966—Davis... .ccccsccscccscscccescceseces 340/5 T
`
`
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`fier output actuates a Schmitt trigger which in turn op-
`1,935,744
`ccccccccccceseccccccaces 325/22
`11/1933) Holden wc
`
`
`
`
`
`
`
`3,189,691 6/1965=Simpson... eee 179/1 VE
`erates a transmitter enablé-receiver disable switching
`
`
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`TIN947 Atkins oo. cllecceecccesenees 179/1 VC
`2,424,216
`
`
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`
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`circuit. Delay meansare provided so that the transmit-
`
`3,646,576 2/1972—Griggs.....csssccccsseceeecees 179/1 SA
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`
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`ter does not turn off during brief intersyllabic pauses.
`FOREIGN PATENTS OR APPLICATIONS
`
`
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`13 Claims, 2 Drawing Figures
`
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`
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`3/1943 Germany... 179/121 C
`734,732
`
`
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`OTHER PUBLICATIONS
`
`
`
`
`
`Gazey and Morris, An Underwater Acoustic Telephone
`
`
`
`
`for Free-Swimming Divers, Electronic Engineering,
`
`
`
`
`
`
`Vol. 36, No. 436, 6/1964 p. 364-368.
`
`
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`
`
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`Primary Examiner—Kathleen H. Claffy
`
`
`
`
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`Assistant Examiner—Jon BradfordLeaheey
`
`
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`
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`Attorney —C. Yardley Chittick, Richard J. Birch et al.
`
`ABSTRACT
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`1/6
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` “2
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`Page 1 of 8
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`GOOGLE EXHIBIT 1007
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`Page 1 of 8
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`GOOGLE EXHIBIT 1007
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`PATENTED Ju 1 7 ta2s
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`Page 3 of 8
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`Page 3 of 8
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`

`

`3,746,789
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`1
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`TISSUE CONDUCTION MICROPHONEUTILIZED
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`TO ACTIVATE A VOICE OPERATED SWITCH
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`BACKGROUNDOFTHE INVENTION
`
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`The present invention relates to communication sys-
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`tems in general and, more particularly, to a voice-
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`activated transmit switch for high noise environment
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`voice communication systems.
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`The use of voice activated transmit switches (VOX)
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`in communication systemsis well known. In such sys-
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`tems, the output from a speech microphoneis used to
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`actuate a circuit which enables the transmitter while at
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`the same disabling the receiver. However, this type of
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`system is highly susceptible to false keying of the trans-
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`mitter by non-speech noises. The problem offalse key-
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`ing of the transmitter is particularly acute in underwa-
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`ter communications systems where the diver’s breath-
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`ing noises and gas flow noises may actuate a standard
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`VOXcircuit. Similar problems also occurin other high
`noise environments.
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`It is, therefore, a general object of the present inven-
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`tion to provide a voice actuated transmitter switch or
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`VOX that is substantially insensitive to non-speech
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`generated sounds.
`25
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`It is a specific object of the present invention to pro-
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`vide a voice actuated transmit switch for use in a high
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`noise environment voice communication system.
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`It is another objectof the invention to provide a voice
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`actuated transmit switch which is especially suited for
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`underwater communication systems.
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`It is still another object of the invention to provide a
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`voice actuated transmit switching circuit which is in-
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`sensitive to breathing noise.
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`is a feature of the invention that the circuitry
`It
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`thereof can be easily incorporated in existing commu-
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`nication systems.
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`It is still another feature of the invention that opti-
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`mum speech intelligibility is maintained while at the
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`same time providing for voice actuation of the commu-
`40
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`nication system transmitter in a high noise environ-
`ment,
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`These objects and other objects and features of the
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`invention will best be understood from a detailed de-
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`scription of a preferred embodimentthereof, selected
`45
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`for purposesofillustration, and shownin the accompa-
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`nying drawings, in which:
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`FIG. 1 is a block diagram of a communication system
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`utilizing the voice actuated transmit switch ofthe pres-
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`ent invention; and,
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`FIG. 2 is a schematic diagram of the VOXcircuit.
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`Turning now to the drawings,
`the voice actuated
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`switch or VOX of the present invention will be de-
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`scribed in connection with an underwater communica-
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`tions system shownin block diagram form in FIG. 1 and
`55
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`indicated generally by the reference numeral 10. It
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`should be understood that the description of the inven-
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`tion in connection with the underwater communica-
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`tions system is by way ofillustration only and that the
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`voice-activated transmit switch can be used in other
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`communication systems andthatit is particularly suited
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`for high noise environment communication systems.
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`Looking at FIG. 1 which depicts the illustrative un-
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`derwater communications system, the diver interface
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`comprises a speech cavity 12 and a speech microphone
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`14, Preferably, the speech microphone 12 is a high-
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`impedance, piezo electric unit which is suitable for the
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`underwater use. The microphone is enclosed in the
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`speech cavity 12 which surrounds at least the diver’s
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`mouth in order to provide a gas space into which the
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`diver can articulate speech in a more or less normal
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`fashion. The speechcavity is also connected to the div-
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`er’s breathing apparatus 16 so that the acoustic input
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`to the cavity is a mixture of speech occurring at random
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`intervals and gas flow and breathing noises occurring at
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`moreorless regular intervals.
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`The speech cavity 12 has sharp, well-defined reso-
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`nancestypically below 1000 hz, which cause the acous-
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`tic output of the diver’s vocal track to rise at a rate of
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`roughly 12 decibals per octave below that frequency.
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`This abnormal frequency response in the speechsignal
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`seriously impairsintelligibility. A speech processor, in-
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`dicated generally by the reference numeral 18,is em-
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`ployed to electrically modify the speech signal from the
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`speech microphone 14 in such a way that resonances
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`are removed, the power content of the signal is in-
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`creased and theintelligibility in noise is improved. The
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`speech processor 18 comprises a speech pre-amplifier
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`20, a highpassfilter 22, and a speech amplifier/clipper
`24,
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`The implementation of the circuitry of the speech
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`pre-amp, highpass filter and speech amplifier/clipper
`are well-knownin the art and need not be described in
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`detail. However, preferably the speech pre-amplifier 20
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`comprises a junction field-effect transistor connected
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`as a common-source amplifier having a gain of approxi-
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`mately 20 decibels from 500 to 10,000 hz., with an
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`input impedance of 1 megohm. The function of the
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`speech preamplifier 20 is to boost the output of the
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`speech microphone14 to approximately 500 mV peak-
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`to-peak for further processing.
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`The active highpass filter 22 comprises a fourth-
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`orderfilter having a Butterworth response with a cor-
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`ner frequency of 1100 hz. It comprises two second-
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`order sections in series, synthesized by meansof RCel-
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`ements and unity-gain source-follower JFET amplifier.
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`Since the speech information below 1000 hz are em-
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`phasized by the speech cavity 12 at a rate of 12 decibels
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`per octave, the output of the highpassfilter is a speech
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`signal
`in which components below the corner fre-
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`quencyroll off at a rate of ~-12 decibels per octave.
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`This type of frequency response results in virtually
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`complete elimination ofthe first formant of the speech
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`signal, which is not essential to good intelligibility, and
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`of low-frequencynoisesarising either in the wateror in
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`the speech cavity.
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`The speech amplifier/clipper 24 preferably .com-
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`prises a bipolar transistor connected as a common-
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`emitter amplifier having a gain of approximately 40
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`decibels. Twosilicon diodesin parallel, but in opposite
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`directions, are capacitively coupled between the base
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`andcollective terminals of the transistor. The resulting
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`non-linear negative feedback allows signals below ap-
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`proximately 10mv peak-to-peak to be amplified with
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`little distortion. Signals above this level are heavily
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`clipped. The maximum output from this stage is ap-
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`proximately 1.2 V p-p, regardless of input level.
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`The neteffect offiltering the speech signal as de-
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`scribed aboveandclippingit is to increase its average
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`power content andits intelligibility in noise by reinforc-
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`ing essential portions of the frequency spectrum. The
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`process of clipping generates harmonics which arere-
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`movedbyan active low-passfilter 26 which is a second-
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`order Butterworth filter having a corner frequency of
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`3.5 khz. This filter is also synthesized with RC elements
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`20
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`50
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`65
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`Page 4 of 8
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`Page 4 of 8
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`3,746,789
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`3
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`4
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`and a unity-gain JFET source-follower. The comerfre-
`duction headphone 52. The input pre-amplifier 40
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`quency of 3500 hzis high enough to preserve frequen-
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`preferably is a low-noise JFET connected as a com-
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`cies which are essential to good intelligibility.
`mon-source amplifier with a gain of approximately 20
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`The transmitter portion of the underwater communi-
`db at the carrier frequency. The amplifier 42 provides
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`cations system indicated generally by the reference nu-
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`60 db of linear gain and the limiter 44 provides approx-
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`meral 28, comprises a voltage controlled oscillator 30
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`imately 40 db of the gain before limiting. The gain and
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`and a tuned power amplifier 32. The linear VCO 30is
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`limiting have been chosen to provide a useful limited
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`set to operate a center frequency of approximately 40
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`signal of at least 100 mv rms with a minimum input of
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`khz. The function of the VCO is to provide a frequen-
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`1 microvolt rms from the transducer 34.
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`cy-modulated carrier. Its transfer characteristic is such
`The bandpass filter 46 is a simple parallel-tuned LC
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`that changes in control voltage of plus or minus 1000
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`resonant circuit placed at the output ofthe limiter 44
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`mV cause the center frequency to change by plus or
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`in order to restore the sinusoidal character of the sig-
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`minus 3.5 khz. Thus,if the maximum speech frequency
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`nal. The output from the bandpassfilter 46 is applied
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`to be transmitted is 3.5 khz the modulation index is 1.0
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`to the phase-locked loop 48 which is used as a fre-
`15
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`and the speech signal can be transmitted usingatotal
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`quency demodulator. The VCO of the phase-locked
`bandwidth of 7 khz.
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`loop is set to operate at approximately 40 khz, and its
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`The tune power amplifier 32 preferably comprises a
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`low-passfilter elements are chosen to provide a capture
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`single-transistor class-C tuned power amplifier. The
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`range ofat least plus or minus 4 khz. This allows the de-
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`amplifier delivers 500 mW ofelectrical power into a
`modulator to lock onto any signal whose frequencyis
`20
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`1000-ohm resistive load. Since the output of the volt-
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`within 10 percent of the nominal carrier frequency.
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`age controlled oscillator 30 is a square wave the input
`This relatively large capture range makes it possible to
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`of the tuned amplifier contains a series resonant circuit
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`utilize simple RC oscillators in the transmitter, since
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`to eliminate harmonics of the desired carrier fre-
`frequency stability is unimportant.
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`quency. A tuned transformer matches the collector of
`The output of the phase-locked loop 48 drives an
`25
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`the transistor to a transducer 34. The secondary of the
`audio amplifier 50 having a maximum poweroutputof
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`transformer is designed to resonate at the carrier fre-
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`150 mW andasensitivity of 45 mV rmsfor pull-power
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`quency of 40-khz with a 3-db bandwidth 7 khz, corre-
`output. The audio amplifier is transformer coupled to
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`sponding to an effective Q of 5.72. The output of the
`a high-impedance piezo-electric bone -conduction
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`tuned poweramplifier 32 is connected througha trans-
`headphone 52 which couples the audio signal into the
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`diver’s ear.
`mit receive gate 36 to the previously mentioned trans-
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`ducer 34, The transducer is a resonant, air-filled tubu-
`Having briefly described the speech microphone,
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`lar ceramic transducer whose dimensions and material
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`transmitter, and receiver portions of the underwater
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`are chosen to resonate at the carrier frequency in the
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`communications system 19, I will now describe in detail
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`radial mode of vibration. The length-to-diameter ratio
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`the voice-activated transmit switch circuitry. It is im-
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`is approximately 1, so as to provide somedirectionality
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`practical to maintain the transmitter portion of a com-
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`in planes parellel to the longitudinal axis of the trans-
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`munication system continuously activated since it con-
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`ducer. The transducer is capped to increase its receiv-
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`sumes much more powerthan any other portionof the
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`ing sensitivity and it is encapsulated in a thin sheet of
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`system. On the other hand, manual activation of a
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`sound-transparent material so as to render it water-
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`switch for transmission would require a working diver
`40
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`proof and capable of operating in at least 250 feet of
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`to maintain one hand available for this purpose. This
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`sea water. The static capacitance of the transducer 34
`may not be possible at all times and thus may prevent
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`is used as part of the capacitance necessary to tune the
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`the diver from being able to communicate duringa crit-
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`ical situation.
`secondary winding of the tuned power amplifier output
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`transformer so that a separate tuning coil is urneces-
`A voice-operated transmit switch (VOX) is desirable
`45
`sary.
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`in such a communications system. However, it is not
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`Since the power amplifier operates in the class-C
`possible to use the output of the speech microphone 14
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`mode, it is unnecessary to disconnectit from the tuned
`for VOX purposes, since it contains breathing ‘noises
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`transformer during reception, because the reverse-
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`which would activate the transmitter 28 every time the
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`biased transistor becomesa resistor having a resistance
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`diver inhales or exhales. Furthermore, it is not possible
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`which is several orders of magnitude larger than the
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`to discriminate against these noises on the basis of
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`resonant resistance of the transducer 34.
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`acoustic levels alone, since these noises are of at least
`The transducer 34 is also used for the detection of
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`the samelevel as speechsignals. If a VOX system is set
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`acoustic signals for reasons of economyand simplicity.
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`so that it will not be activated by these noises, a diver
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`The receiver input, therefore, must be effectively dis-
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`would have to shout into the microphone to make the
`55
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`connected from the transducer during transmission.
`system operate. It is not possible to discriminate against
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`This is accomplished by the previously mentioned
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`these breathing noises on the basis of frequency alone
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`transmit/receive gate 36 which comprises a carrier-
`either since their frequency spectrum is rather wide
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`and erratic.
`activated series/shut analog gate having an inductor,
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`two pairs of switching diodes, a series tuning compaci-
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`Various solutions have been proposed to this prob-
`60
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`tor and a parallel tuning capacitor connected so as to
`tem. Some form of frequency analysis is usually em-
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`block the signal from the input of the receiver during
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`ployed to distinguish noise from speech, but the com-
`transmission.
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`plexity required to makethis solution rather unenomi-
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`The receiver section of the underwater communica-
`cal for use in a self-contained miniature communica-
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`tions system, indicated generally by the reference nu-
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`tions system of the type shown in FIG. 1.
`65
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`meral 38, comprises an input pre-amplifier 40, an am-
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`The present
`invention utilizes a separate tissue-
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`plifier 42, a limiter 44, a band-pass filter 46 a phase-
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`conduction microphone 54 to generate a transmitter
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`locked loop 48, an audio amplifier 50 and a bone con-
`keying signal. Preferably, the tissue conduction micro-
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`30
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`50
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`Page 5 of 8
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`Page 5 of 8
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`3,746,789
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`§
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`phone 54is a throat microphone whichis located in the
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`vicinity of the larynx ofthe diver, in such a position that
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`the tissue vibrations due to modulation of the vocal
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`chords (speech) have a much higher amplitude than
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`those due to gas flow or breathing and swallowing
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`noises. However,
`the tissue conduction microphone
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`also can be placed against the chest cavity to detect the
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`speech sounds. The detection of the speech soundsat
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`very favorable signal-to-noise ratios makes it possible
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`to discriminate against unwantednoises on the basis of
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`amplitude alone, without having to resort to more elab-
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`orate signal processing techniques. At the sametime,
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`optimum speechintelligibility is assured by the use of
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`the separate speech microphone 14 positioned directly
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`in front of the mouth of the diver.
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`The tissue-conduction throat microphone 54 should
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`be in good contact with the diver’s neck tissue. The op-
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`timum location varies from individual to individual and
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`it must be determined by each individual by trial and
`20
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`error. This is usually a one-time operation whichis eas-
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`ily performed in the water. The throat microphone 54
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`is isolated from waterborne noises by a layer of sound
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`absorbing material 56. Preferably the sound absorbing
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`material 56 comprises a layer of 3/16 inch mark cellu-
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`lar rubber or neoprene of the type normally used to
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`construct wet diving suits. If the diver wears a diving
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`hood of this material, the best location for the throat
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`microphoneis underthe neck portion of the hood. Oth-
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`erwise, a simple holder (not shown) is used to maintain
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`the microphonein place and to provide acoustical iso-
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`lation from the water.
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`The output from the throat microphone §4is applied
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`to a bandpass filter 58 having a center frequency
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`slightly below 1 khz and a passband of 40 to 100 hz.
`35
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`The purpose of the bandpass filter 58 is to eliminate
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`high or low-frequencynoises, either waterborne or gen-
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`erated by the diver which may accidentally trigger the
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`VOX system. Thisfilter is particularly important when
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`the diveris using a single-hose demand regulator hav-
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`ing an exhaust port only a few inches away from the
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`throat microphone,since the noise generatedbythe ex-
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`haust bubbles would otherwise cause the VOX system
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`to operate every time the diver exhaled.
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`The output from bandpassfilter 58 is applied to a
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`high gain amplifier 60 which providessufficient gain to
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`amplify the signal from the bandpassfilter to a level
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`sufficient to drive an audio detector 62. The output
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`from the amplifier 69 is rectified by the combination of
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`diode 64 and capacitor 66 (FIG. 2) to produce a DC
`50
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`level at the input of Schmitt trigger 68. The value for
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`resistor 76 and the smoothing capacitor 66 are chosen
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`so that the resulting time constant is less than 500 mi-
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`croseconds, to assure fast actuation of the VOX sys-
`tem.
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`Looking at FIG. 2, the Schmitt trigger circuit 68 has
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`a high input impedance, an upper trip point of approxi-
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`mately 1.2 V, and a hysteresis of approximately 0.2 V.
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`The function of the Schmitttriggeris to provide sharply
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`defined ON/OFFlevels and some degree of immunity
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`to low-level random noise inputs. The output of the
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`Schmitt trigger 58 is used to activate a receiver power
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`switch 72 and a transmitter power switch 74. These
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`switches comprise PNP transistors which are con-
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`nected to the positive power supply and are activated
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`by the combination of inverters shown in FIG. 2 so that
`
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`the receiver power is OFF when transmitter poweris
`ONand vice versa.
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`45
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`6
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`A resistor 76 is used to couple the outputof the audio
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`detector 62 to the input of the Schmitt trigger 68, The
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`value of this resistor is chosen to provide a delay of ap-
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`proximately 0.2 secondsafter the rectified audio signal
`is removed, so that the transmitter does not turn off
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`duringbrief intersyllabic pauses. Thetotal time elapsed
`betweenthestart of the word and full activation of the
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`transmitter is approximately 1 millisecond given the
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`circuitry shown in FIG, 2. Since the average syllabic
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`length is approximately 24 milliseconds, there will be
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`no loss of syllables during normal conversation.
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`The primary advantage of using an underwater
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`speech communication system is the enhancement of
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`diver safety, resulting from the capability of the diver
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`to inform others of his own situation, and of others to
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`recognize potential dangeroussituations from informa-
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`tion supplied by the diver. In a case of portable commu-
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`nication devices, however,it is not practical to main-
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`tain the diver’s transmitter activated continuously. Cer-
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`tain types of diving accidents may take place during
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`diver silence periods. A specific exampleis the loss of
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`consciousness due to low oxygen concentration in the
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`breathing medium whichtakes place in a very gradual
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`mannerand usually goés unnoticed by the victim. If an
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`unconsciousdiveris not within visual range and imme-
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`diate reach ofthe other divers, his problem may go en-
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`tirely unnoticed until it is too late for rescue.
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`Onesolutionto this problem is to use telemetry tech-
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`niques for monitoring diver physiological functions by
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`sensing cardiac rhythm, blood pressure, and body tem-
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`perature or environmental conditions, such as breath-
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`ing medium pressure or partial pressure ofcritical
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`gases. The technology for accomplishing this type of
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`monitoring exists at the present time, but the equip-
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`ment requiredis usually so expensive asto be justifiable
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`only whenthe objective of monitoringis the acquisition
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`of bio-medical data.
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`In my co-pending application,filed of even data here-
`with, and entitled PHYSIOLOGICAL ALARM SYS-
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`TEM, there is described an alarm system whichis espe-
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`cially suited for an underwater communication system.
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`The alarm system monitorsthe diver by meansoffacili-
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`ties already present in the underwater communications
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`system and evaluates the data within the system itself
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`and triggers the transmission of the alarm signal only
`when anomalous conditions are detected. The alarm
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`system is shown in block diagram form in FIG. 1 and
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`will be briefly described in order to showits interrela-
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`tionship with the VOX system of the presentinvention.
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`The speech microphone 14 is exposed to speechsig-
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`nals which are generated at random intervals, and to
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`breathing and gasflow noises which take place at regu-
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`lar intervals. The time distribution of diver-generated
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`signals which are conveniently present at any point in
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`the speech processor 18, can be used as a means of de-
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`tecting anomalous respiratory conditions.
`it is obvious that the diver must breathe at least once
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`during a certain period of time from which a definite
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`upper bound T, exists regardless of exertion level and
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`individual breathing habits. If a signal is not produced
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`within this period of time, the diver may be assumed at
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`best to be breathing too slowly, or at worst,
`to have
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`stopped breathing altogether.
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`Similarly, the diver or his breathing equipment must
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`be silent at least once during the breathing cycle or at
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`the end of sentences during the generation of speech.
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`Thus, another upper boundT, exists for the maximum
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`55
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`Page 6 of 8
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`Page 6 of 8
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`7
`8
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`duration of a diver-generated signal. If this upper band
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`26 and 30 is deactivated while the input section of the
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`is exceeded, the diver may be assumedto be breathing
`VOX system comprising bandpassfilter 58, amplifier
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`abnormally. This condition may come about, for exam-
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`60 and audio detector 62 are activated. Thus, when the
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`ple, if a demand regulatorfails and delivers a continual
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`diver s